1. Field of the Invention
The invention relates to an antenna unit and a portable electronic apparatus.
2. Description of the Related Art
In various electronic apparatuses including an electronic watch, a wireless charging system using, for example, electromagnetic induction, without direct connection to a charger through a wire, is widely available.
A charger for wireless charging includes a power supply coil and a cover plate which covers the power supply coil. Meanwhile, an electronic apparatus includes a power receiving coil in a housing.
When the electronic apparatus approaches the cover plate in a state in which a current is applied to the power supply coil of the charger, electromagnetic induction occurs between the power supply coil and the power receiving coil and power (induced electromotive force) is generated on the power receiving coil side. In the electronic apparatus, charging of a built-in battery in the electronic apparatus is performed with the power generated in the power receiving coil.
Here, in order to enhance charging efficiency, it is preferable that the power supply coil and the power receiving coil approach each other as close as possible. Accordingly, the electronic apparatus, for example, may have a flat surface as a surface on a side on which the power receiving coil is provided, the electronic apparatus may be mounted on the cover plate of the charger, and the electronic apparatus may come into direct contact with the cover plate.
Incidentally, in various electronic apparatuses, various uneven shapes are often formed on the side on which the power receiving coil is provided. For example, in the case of the wristwatch-type electronic watch, the power receiving coil is accommodated in a main body case together with a movement which drives the watch. In the main body case, a belt connecting section, to which a belt for wearing the wristwatch-type electronic watch on a wrist is connected, is provided. In general, the belt connecting section is provided to obliquely protrude from the main body case. Thus, since a case back surface of the main body case and the belt connecting section have a shape of the surface of the wrist, a sense of stability or wearing sensation is enhanced when the wristwatch-type electronic watch is worn on the wrist.
Incidentally, when the belt connecting section obliquely protrudes, the belt connecting section comes into contact with the cover plate when the wristwatch-type electronic watch is mounted on the cover plate of the charger. Therefore, a gap is formed between the case back surface of the wristwatch-type electronic watch and the cover plate of the charger, a distance between the power supply coil and the power receiving coil is increased, and thus charging efficiency is lowered.
For example, JP-A-6-188809 discloses a configuration in which a lid member including a built-in coil (antenna) is provided on a surface side of the main body case of a wristwatch and the lid member is linked to the main body case through a hinge so as to be openable and closable.
In the configuration, the lid member is closed and opened, and thereby it is possible to adjust a position of the coil with respect to the main body case. The coil in JP-A-6-188809 is used in a communication system; however, the coil is replaced with the power receiving coil for charging. Hence, during the charging, it is considered that the position of the power receiving coil is adjusted in the state in which the lid member is opened, the power supply coil and the power receiving coil approach, and thus it is possible to enhance the charging efficiency.
However, in the configuration as disclosed in JP-A-6-188809, in order to cause the power receiving coil provided in the lid member to approach the power supply coil of the charger, during the charging, the wristwatch needs to be turned over in a state in which the lid member is opened and needs to be mounted on the cover plate of the charger.
However, when the wristwatch-type electronic watch in the state of being turned over is mounted on the cover plate of the charger, it is not possible to visually recognize a display unit in a case of checking the time during the charging. Such a problem is not limited to the wristwatch-type electronic watch, but arises similarly as long as the electronic apparatus includes a display unit.